The present invention generally relates to an ignition apparatus for an internal combustion engine. More specifically, the present invention is directed to a waterproof spark plug hole cap of an ignition apparatus.
In FIG. 1, there is schematically shown a sectional view of the conventional ignition apparatus for the internal combustion engine disclosed in Japanese Laid-open Utility Model Application No. 5-21175. In this drawing, reference numeral 1 shows a decorative cover, reference numeral 2 indicates an ignition coil, reference numeral 2a represents a lower surface of an ignition coil case, and reference numeral 3 denotes a cylinder head cover of an internal combustion engine for fixing the ignition coil 2. Also, reference numeral 3a is an upper surface of the cylinder head cover 3, reference numeral 3b shows a plug hole inlet portion having a shape of a projected portion having a shape of a projected ring, and formed on an upper edge portion of the cylinder head cover 3, reference numeral 4 shows an ignition (spark) plug positioned on the cylinder of the internal combustion engine, reference numeral 4a indicates a plug gap projected into an inside of a combustion room of the internal combustion engine, and reference numeral 5 represents a plug hole of the cylinder head cover 5 for storing the ignition plug 4 at a bottom thereof. Reference numeral 6 is a plug hole cap sealed at an upper portion of the plug hole inlet portion 3b, reference numeral 6a indicates a lid-shaped portion for covering the plug hole inlet portion 3b, and is closely fitted to the plug hole inlet portion 3b by way of elastic recovery force of rubber, reference numeral 6b shows a second water resistant (waterproof) seal portion formed at a peripheral portion of the plug hole cap 6 with being projected from the plug hole cap 6, and having a function used to center the plug hole 5 and the plug hole cap 6. Furthermore, reference numeral 6c shows a cylindrical-shaped portion projected upwardly from the lid-shaped portion 6a, and reference numeral 6d is an air bleeding hole, or a purge hole penetrating from the center of the cylindrical-shaped portion 6c via the plug hole cap 6 to the plug hole 5, and also reference numeral 6e is an outlet of the air bleeding hole 6d.
A description will now be made of operations. When water happens to enter into the plug hole 5, water components would penetrate from the surfaces located along the connection boundary. As a result, the high voltage withstanding performance cannot be maintained, the high voltage leaks into the inner wall 3c of the plug hole 5, and then discharge failure occurs in the plug gap 4a, so that the internal combustion engine cannot be brought into the normal operation condition.
Therefore, it is required to avoid that water or water components enter from the upper surface 3a of the cylinder head cover into the lid-shaped portion 6a of the plug hole cap 6 and the second water resistant seal portion 6b. It should be noted that in response to the drive and stop operations of the internal combustion engine, the temperature in the plug hole 5 is greatly changed, and then air inside the plug hole 5 is expanded and contracted. When this contraction level would become large, water would enter from the seal portion into the plug hole 5. Accordingly, to cause air to flow in/out from the plug hole 5, the air bleeding hole outlet 6e is formed at a position where no water may enter.
As conditions under which the plug hole cap 6 is wetted by water, or water enters into the plug hole cap 6, there are such cases that the plug hole cap 6 is wetted by scattered water mixed into the engine room while the vehicle is driven in the rain, and reserved water flowing over the upper surface of the cylinder head enters from the seal portion. When there is a small amount of the scattered water, this scattered water is shielded by the lower surface 2a of the ignition coil case located just above the plug hole cap, so that the scattered water does not enter from the air bleeding hole outlet 6e. With respect to the reserved water, since the air bleeding hole outlet 6e is located higher the upper surface 3a of the cylinder head cover, the water reserved at the upper surface 3a of the cylinder head cover does not flow therein. However, when there are large amounts of scattered water, this scattered water cannot be shielded. Also, when the water level of the reserved water at the upper surface of the cylinder head cover exceeds the air bleeding hole outlet 6e, this reserved water will enter. Thus, to limit the wetted amount of water, either the decorative cover 1 is mounted, or the water exhausting path is formed in the cylinder cover 3 and further the upper surface 3a is inclined, so that an increase of the water level is prevented.
Since the conventional plug hole cap portion of the internal combustion engine is constructed of the above-described structure, as to the scattered water, a large amount of which directly flows from the upper portion of the ignition coil into this plug cap portion, the air bleeding hole outlet is directly wetted by the scattered water and thus there is no way to avoid that the scattered water enters therein. Also, as to the reserved water caused by entering a large amount of water, the position of the ignition coil must be set to the higher position in order to set the position of the air bleeding hole outlet. However, there is such a problem to employ the above-described structural modification in very narrow engine rooms developed in recent years.
Moreover, there is a current trend to discontinue the use of decorative cover in recent automobiles in order to reduce the manufacturing cost. On the other hand, there is another problem that since, for instance, a cooling air intake inlet for an inter cooler is formed in a bonnet of a vehicle with a turbocharger, rainwater would directly enter into engine room.